Definition

Noun: * Newton's third law of motion: The principle in physics stating that for every action (force) there is an equal and opposite reaction (force). When one object exerts a force on a second object, the second object simultaneously exerts a force equal in magnitude and opposite in direction on the first object.

Usage

This term is used almost exclusively in scientific contexts, particularly in physics and engineering, to describe a fundamental law of motion. * It explains the mechanics behind propulsion, collisions, and many everyday phenomena. * It is often cited in its full form, Newton's third law of motion, or simply as the third law.

Examples

• The law of action and reaction explains how a rocket propels itself forward by expelling exhaust gases backward.
• When you push against a wall, the wall pushes back on you with an equal force; this is a demonstration of the law of action and reaction.
• According to the law of action and reaction, the force a swimmer applies to the water is matched by the force the water applies to propel the swimmer forward.

Advanced Usage

• Conceptual Application: The principle is sometimes referenced metaphorically outside of physics to suggest that events or decisions can have direct and opposite consequences.
  • In geopolitics, some analysts describe sanctions as an action that often produces a reaction in the form of counter-sanctions.

Variants and Related Words

• Newton's third law (of motion): The most common and precise synonym.
• Third law: A common abbreviated form used in technical discussions.
• Action-reaction principle: A descriptive alternative name.

Synonyms

• Newton's third law
• Action-reaction principle

Related Idioms or Phrases

• For every action, there is an equal and opposite reaction: This is the colloquial, proverbial phrasing of the law, often used even in non-scientific contexts to imply inevitable consequences.
  • He spread rumors about his colleague, but for every action, there is an equal and opposite reaction—soon, people began to question his own credibility.

Noun

1. action and reaction are equal and opposite